1. Field of the Invention
The present invention relates in general to disc cassettes for use in a photo-electromagnetic disc player, and more particularly to the disc cassettes of a type having a shutter.
2. Description of the Related Art
In order to clarify the object of the present invention, one conventional disc cassette DC of the above-mentioned type will be described with reference to FIGS. 9A and 9B of the drawings which figures show front and back perspective views of the disc cassette DC, respectively.
The disc cassette DC shown in the drawings is of a type which writes and read information onto and from a photo-electromagnetic disc using so-called xe2x80x9cmagnetic modulation overwrite methodxe2x80x9d. The disc cassette DC comprises a rectangular case 1 in which a photo-electromagnetic disc 2 is rotatably installed. To a center portion of the disc 2, there is fixed a hub 2a which, upon need of playing the disc 2, is held by a chucking member of a disc player (not shown). The case 1 comprises an upper half part 1a and a lower half part 1b which are coupled to have a thin space defined therebetween. As is seen from FIG. 9B which shows a back view of the disc cassette DC, the lower half part 1b is formed at its side rear portions with respective positioning openings 3. Upon insertion of the disc cassette DC into the disc player, positioning pins of the disc player are brought into engagement with the positioning openings 3, thereby to position the disc cassette DC relative to the disc player. The lower half part 1b of the case 1 has near one of the positioning openings 3 a slot in which a miss-write protection pawl 4 is slidably received. When the pawl 4 is moved to one given position, the disc 2 is prevented from recording or writing information thereon. The case 2 is formed at its side front portions with cassette pulling grooves 5. That is, when the disc cassette DC is inserted into a certain position of the disc player, cassette pulling pins of the player become engaged with the grooves 5 and pull the disc cassette DC to a certain bottom position of the disc player.
As is seen from FIGS. 9A and 9B, the upper and lower half parts 1a and 1b of the case 1 are respectively formed with rectangular openings 6a and 6b through which upper and lower surfaces of the disc 2 are partially exposed. The lower opening 6b is larger than the upper opening 6a and is so sized as to expose the hub of the disc 2.
Each opening 6a or 6b has a bridge 1e defined by the case 1, which extends across a mouth portion of the opening, as shown.
A slide bar 8 is mounted on a front edge 1C of the case 1 in a manner to slide in the direction of the arrow xe2x80x9cAxe2x80x9d. Connected to the slide bar 8 is a shutter 7 which comprises upper and lower shutter plates 7a and 7b. Thus, in response to the sliding movement of the slide bar 8, the upper and lower openings 6a and 6b are selectively closed and opened by the upper and lower shutter plates 7a and 7b. Although not shown in the drawings, a torsion spring is installed in the case 1 to bias the shutter 7 in the direction to close the openings 6a and 6b. FIGS. 9A and 9B show a condition wherein the shutter 7 assumes its full open position. The slide bar 8 has a thickness somewhat smaller than that of the disc 2 in the case 1.
FIG. 10 shows a condition wherein the disc cassette DC is properly set in the disc player. Under this condition, the shutter 7 of the disc cassette DC assumes its full open position and the hub 2a of the disc 2 is tightly held by the chucking member (not shown) of the disc player. Upon energization of a spindle motor (not shown) by which the chucking member is driven, the disc 2 is rotated about its axis. Within the disc player, there are installed a magnetic head 28 and an optical head 29 which are arranged to put therebetween the disc 2. These heads 28 and 29 face the upper and lower openings 6a and 6b of the case 1, respectively, and are mounted on a same head carriage 24 which is linearly movable in the direction of the arrow xe2x80x9cBxe2x80x9d in FIG. 10, that is, in the radial direction of the disc 2. The head carriage 24 moves between an outermost position as shown by a phantom line and an innermost position as shown by a solid line. Due to movement of the carriage 24, the two heads 28 and 29 are slid radially along the upper and lower openings 6a and 6b while making an interaction therebetween to write or read information on or from the disc 2.
Usually, the disc players used as a supplemental memory device of a computer are restricted by size. As is seen from FIG. 10, assuming that the length of the disc player is xe2x80x9cLxe2x80x9d and a part xe2x80x9cL0xe2x80x9d of the length xe2x80x9cLxe2x80x9d represents the length of a space for containing other mechanisms, the head carriage 24 has to be arranged within a limited zone having the length xe2x80x9cL1xe2x80x9d. The length of an arm 27 through which the head 28 is connected to the head carriage 24 is so determined that when the head carriage 24 is located at the outermost position as shown by the phantom line, the head 28 is located at the outermost recording position of the disc 2. Thus, the innermost position of the head 28 is automatically determined when the head carriage 24 comes into abutment with the slide bar 8 of the disc cassette DC. However, in this case, it sometimes. occurs that the innermost recording area (i.e., the area having the width xe2x80x9cExe2x80x9d) of the disc 2 cannot be practically used, due to the limited movement of the heads 28 and 29 in the inward direction.
It is therefore an object of the present invention to provide a disc cassette which can provide the head carriage of the disc player with a more satisfactory moving area, thereby permitting effective usage of the recording area of the disc.
According to a first aspect of the present invention, there is provided a disc cassette which comprises a case in which a disc recording medium is rotatably received, the case having an opening through which at least an information recording area of the medium is exposed; a bridge defined by the case, the bridge extending across a mouth portion of the opening; a slide bar arranged beside the bridge in a manner to move axially therealong; and a shutter connected to the slide bar to move therewith, the shutter selectively opening and closing the opening in accordance with axial movement of the slide bar, wherein the slide bar has a base portion which comes beside the bridge when the shutter takes the open position, the base portion being formed with a recess which faces in a direction away from the center of the disc recording medium.
According to a second aspect of the present invention, there is provided a disc cassette which comprises a case in which a disc recording medium is rotatably received, the case having an opening through which at least an information recording area of the medium is exposed; a bridge defined by the case, the bridge extending across a mouth portion of the opening; a slide bar arranged beside the bridge in a manner to move axially therealong; and a shutter connected to the slide bar to move therewith, the shutter selectively opening and closing the opening in accordance with axial movement of the slide bar, wherein the slide bar comprises a base portion which comes beside the bridge when the shutter takes the open position and a projection which is to be pressed by a shutter opening pin of a disc player, the projection protruding outward from the base portion.